The invention relates to the re-refining of used motor oil.
Extensive work has been reported in the patent literature on use of large amounts of hot, high pressure hydrogen for vaporization of used motor oil (UMO). While such processes are certainly technically feasible, there are significant capital costs associated with the relatively high pressure operation reported (typically 500 psig). Operation at high pressure makes it difficult to vaporize the used lube oil components, so higher hydrogen addition/circulation rates are used to facilitate vaporization, with hydrogen circulation rates of 10,000-18,000 SCFB being reported. Hydrogen helps suppress some condensation coking reactions that otherwise could occur in the heating and vaporization step. The hydrogen is also present in an amount sufficient to supply the hydrogen demand of a downstream hydrotreating reactor. This combination, high-pressure hydrogen coupled with downstream hydrotreating, can produce a liquid product from a UMO fraction which is excellent for use as either a lube stock or as cracker charge.
Representative hot hydrogen UMO processes are listed below:
While this approach is excellent in terms of product quality, the capital and operating expense of such an approach are significant.
While there has been extensive use of high pressure hydrogen for vaporization and subsequent hydrotreating of UMO, such a process has never been used for simple vaporization at relatively low, pressure.
We wanted a process that could be used to thermally process/vaporize UMO by direct injection of superheated vapor. While we wanted to inject vapor, we also wanted to reduce or even eliminate the costly recycle gas compressor.
We discovered a way to reprocess UMO in a relatively low cost and low pressure facility using direct injection of superheated vapor to heat and thermally process the UMO. We were able, by careful choice of the working fluid and process conditions, to condense much or all of the injected vapor to liquid. A relatively low cost, low energy consuming pump then increased the pressure of the condensed liquid. This high pressure liquid was then subsequently heated and vaporized to form superheated, relatively high pressure vapor for re-injection into the UMO process. We were also able, by selection of different working fluids, to reduce the amount of high-grade (high temperature) heat input required and/or reduce the end of run temperature for the UMO reactor/vaporizer.
Accordingly, the present invention provides a process for direct contact heating and vaporization of UMO comprising heating and vaporizing in a UMO vaporization vessel operating at UMO vaporization conditions a liquid UMO feed by direct contact heat exchange with a recycled, superheated, vapor to produce a UMO vapor fraction comprising a mixture of vaporized lubricating oil boiling range hydrocarbons and said recycled superheated vapor and a liquid phase residue fraction; withdrawing, at least intermittently, from said vaporization vessel said residue fraction as a liquid product of said process; withdrawing from said vaporization vessel, and partially cooling and partially condensing, said UMO vapor fraction and charging same into a hot separator operating at hot separator conditions including a temperature below the boiling point of said lubricating oil boiling range hydrocarbons and above the boiling point of said recycled vapor and separating therein a liquid product phase comprising at least a majority of the lubricating oil boiling range hydrocarbons present in said UMO vapor fraction from a vapor phase comprising at least a majority of said injected, superheated vapor; withdrawing from said hot separator, and cooling and condensing, said hot separator vapor to produce a recycle liquid comprising condensed hot separator vapor condensed liquid; pumping at least a portion of said recycle liquid to increase the pressure thereof and produce a pressurized recycle liquid; heating and vaporizing said pressurized recycle liquid by indirect heat exchange or heating in a fired heater to form superheated vapor; and injecting said superheated vapor into said UMO vaporization process to vaporize by direct contact heat exchange, liquid UMO feed.
In our process, the used lube oil may be treated either continuously or batch-wise. There is nothing critical about the reactor/thermal vaporizer vessel usedxe2x80x94it can be a conventional vapor/liquid contact apparatus such as a modified fractionator, a continuous stirred tank reactor, a turbulent or plug flow reactor, a Wiped Film Evaporator (WFE), or a large pot or vessel. Preferably, multiple batch reactors are used with means for injecting the superheated vapor into a pool of motor oil in each reactor. Hot UMO heating and, if desired, some decomposition of additives can occur in the lower portion of such vessels.
Preferably, the used motor oil is preheated by conventional means such as heat exchange, fired heaters or the like. The temperature of the preheated UMO should not exceed 600xc2x0 F. and preferably does not exceed 500xc2x0 F. and most preferably does not exceed 400xc2x0 F. UMO can decompose on metal surfaces when the temperature gets above 400xc2x0 F.
In a preferred process, wherein the oil is disposed in a batch vessel and contacted with superheated vapor, the vessel overhead will comprise vaporized lubricating oil boiling range components and injected superheated vapor. The overhead vapor fraction is preferably cooled to a temperature sufficient to condense most, and preferably essentially all, of the normally liquid, lubricating oil boiling range components while leaving the injected superheated vapor as a vapor. This permits a condensed, lube oil component rich fraction to be recovered as a liquid from a Hot Flash Separator (HFS). The HFS vapor, comprising 90+mole % and preferably essentially all of the injected superheated vapor, is removed as an overhead vapor fraction from the HFS. This HFS vapor is then cooled to condense at least a portion thereof, and preferably all, to form a liquid phase. This liquid is then pumped to a higher pressure, heated in a conventional fired heater or by heat exchange against some other hot process stream, and re-injected as a recycled, superheated vapor into the thermal reactors processing UMO.
Working Fluid
The xe2x80x9cpumpedxe2x80x9d recycle vapor may aptly be called a working fluid. Suitable working fluids include LPG fractions, such as propane, propylene, butane, isobutylene, and mixtures thereof. These materials have a high heat capacity in terms of energy per mole of gas. They are readily available in a refinery or may be purchased as a staple article of commerce. A drawback to the use of, e.g., propane is that the process must either operate at a relatively high pressure (which impairs UMO vaporization in the thermal reactor/vaporizers) or with cooling water or chilled water to condense the propane vapor into liquid propane which may then be pumped.
Steam may be used, but a significant amount of water treatment may be needed to clean up the condensed, oily water sufficiently to permit its use as boiler feed water to generate superheated vapor. Use of steam will be preferred in some cases, e.g. when the UMO raw feed contains large amounts of water in excess of 1%, e.g. 5-10 or even 15 wt. % or more.
Light alcohols and ethers, which are normally liquids at room temperature, may be used with good results. These materials are cheap and readily available. Even the lightest of them, methanol, may be condensed at ambient temperature at pressures likely to be used in our preferred UMO process. Simple fin-fan coolers, or heat exchangers with cooling water, can condense methanol vapor to form liquid methanol which can be pumped to a higher pressure for re-heating and re-injection into the UMO.
It should be noted that refinery injection of methanol or methanol/stream mixtures is not, per se, novel. Methanol injection is known for use an anti-corrosion aid or as a substitute for steam stripping in a pipe still fractionating crude oil.